In a wireless communication system, by allocating a frequency to a communication device, communication (communication service) of the communication device is enabled. However, at present, it is difficult to allocate frequencies to latest applications and services. The reason is that since predetermined frequency bands are already allocated to various services by a regulatory organization or the like, the spectrum is in a saturation state. In contrast to the saturation state, in reality, there is a frequency band which is not occupied by the spectrum and a load actually applied to the spectrum is not so heavy.
The federal communications commission (FCC) publicly announced a document prepared by the spectrum policy task force (SPTF) in 2002. The document relates to efficient use of the radio spectrum. Concretely, by allowing unlicensed wireless service to an access to a spectrum which is not occupied as described above, efficient use of the radio spectrum is enabled.
One of radio techniques using an unoccupied spectrum is the cognitive radio technique. In a cognitive radio communication system using the cognitive radio technique, first, a secondary user specifies a spectrum which is not temporarily used by a primary user. The primary user is a user licensed to use the spectrum. Subsequently, the secondary user starts communication using the specified radio spectrum. In such a manner, efficient use of the radio spectrum is enabled.
However, in the case where a plurality of secondary users exists, there is a problem such that when the secondary users specify the spectrum and start communication, interference occurs among the plurality of secondary users. Particularly, in the case where a plurality of secondary users belong to networks different from one another or in the case where a plurality of secondary users use communication protocols different from one another, the above-described problem becomes conspicuous.
To solve the above-described problem, for example, a standardization group of IEEE studies how to manage coexistence of a plurality of wireless networks different from each other. As a result of the studies related to such coexistence until now, there is realization of coexistence by a cooperative or uncooperative method in consideration of information exchange among a plurality of wireless networks. An object of such study is mainly a plurality of networks for primary users different from each other (also called legacy wireless networks). An example of coexistence of a plurality of legacy wireless networks different from one another is a network according to IEEE802.11 and a network according to IEEE802.15. Therefore, coexistence of a network including a secondary user with another network has not been sufficiently studied.
In the case of realizing coexistence of a plurality of networks for secondary users, it is necessary to consider another factor different from the coexistence of legacy wireless networks. Concretely, the following points have to be considered and it is not easy to realize the coexistence.
First, to realize the coexistence of a network for secondary users, interference to a network of a primary user has to be considered. Usually, each of the secondary users is constructed to access spectrum which is not temporarily used by the primary users. Consequently, a case such that a plurality of secondary users accesses the same spectrum may happen. When such a case happens, there is the possibility that interference also to the primary user occurs.
Second, even when the coexistence of networks for secondary users is realized, there is the possibility that a network for secondary users has to be reconstructed. A scheme of such a reconstruction has to be considered.
Third, it has to be considered to obtain (or access) information necessary to determine an access to the spectrum. For example, in a cognitive radio communication system, as information necessary to determine an access, there are two kinds of information; sensing information and regulatory information. However, according to non-patent literature 1, the regulatory information is stored in a place different from that of the sensing information. In the case where there is a plurality of pieces of information necessary to determine an access and the information is stored in respective databases, it is not easy to obtain the plurality of pieces of information.